The invention relates to a rope-clamping device comprising two opposing clamping elements equipped with teeth and arranged above a reference surface, the distance between the clamping elements being variable to allow the rope to be inserted and removed, and the distance being reducible by a tensile force which acts up on the rope and presses the clamping elements thereagainst.
Rope-clamping devices have hitherto been used in sail-boats under the exclusive designation of "sheet clamps"; they serve to engage and secure "sheets", as certain ropes in sail-boats are known. In this case the clamping elements are in the form of pivotable jaws and are arranged to move in such a manner that pulling on the rope in one direction tends to narrow the gap between the clamping elements, whereas a pull in the opposite direction increases the gap at least enough to allow the rope to be pulled substantially freely through the device. In this connection, it must also be possible to insert and remove the rope, depending on the sailing manoeuvre to be carried out, as quickly and reliably as possible.
One known sheet-clamp is the so-called "Curry clamp" consisting of two clamping jaws arranged pivotably upon a metal support-plate. The toothed surfaces of the jaws, which face each other, are arranged at an angle to each other, thus presenting a narrow, tapered, V-shaped or dove-tail-shape gap into which the sheet is inserted. The jaws are adapted to pivot outwardly about their axes, thus allowing the gap to be widened to accept the sheet. After the latter has been inserted, the jaws are pivoted back by return springs, the sheet being thus clamped between the toothed clamping surfaces. The clamping action is considerably increased by pulling on the rope in the locking direction of the clamp (known as self-locking). With a sheet-clamp of this kind, it is possible to pull the sheet towards the apex of the V through the gap, whereas a pull towards the open end of the V locks it.
In the case of a clamp of this kind, it is already known to facilitate insertion of the sheet into the clamp by increasing the height of the jaws and by providing the additional clamping surface thus obtained with a series of grooves arranged obliquely one behind the other. These grooves form, at the upper boundary of the clamping surface, a sloping curves plane. When a load is applied to the sheet, it slides, on the sloping plane, into the clamping gap without any tension being applied to the clamping jaws.
Clamps of this kind have a serious disadvantage in that the sheet is very awkward to release in an emergency. In a high wind, the tension on a sheet is frequently several hundred kg, and anyone standing on the other side of the boat requires an enormous lever-action to lift the sheet and thus release it from the clamp. Added to this is the pressure of the clamping jaws on the sheet, and the time lost may often result in capsizing the boat. Furthermore, the sheet is eventually damaged by being snatched out of the toothed clamp and must therefore be replaced after one season at the most.
U.S. Pat. No. 3,677,213 discloses another sheet clamp comprising only a single pivotable clamping jaw by means of which the sheet is clamped, in the locking direction, against a flat surface constituting the clamping-jaw abutment. In order to facilitate removal of the sheet, the end of the clamping jaw is arranged to tilt to a limited extent. However, this is of no assistance in engaging the sheet. The fact that the sheet is clamped on one side only, and that it can slide very easily on the surface facing the jaw, results in very heavy loading, and thus premature wear, of the sheet.